The length of time it takes to get planning permission is affected by the completeness of the application and by whether or not there is an appeal. Generally, a valid application will be dealt with by a planning authority within twelve weeks, from the date the application is made to the final granting of permission. However, the period can vary, particularly if the planning authority seeks further information from the applicant (which must be done within the first eight weeks).
The planning authority then has four weeks from the day the further information is received to make a decision on the application. The following table illustrates the timescale involved in most cases.
Cork Co Co will generally inform you of the decision after 8weeks but will wait a further 4weeks before issuing their decision formally. I would imagine all LA have a similar system. If you call the planning office they will confirm their timescale and inform you of any delays/backlog which they may have. I found the counter staff in Cork Co Co very helpful.
Good Luck